A string class that don't stretch

[craigkenisston]

I need an special string that have a fixed capacity and that
automatically(silently) trims extra space.

MySpecialString str = new MySpecialString(10);

str = "1234567890ABCDE"

Console.WriteLine(MySpecialString.ToString())
// output "1234567890" i.e. trimes the "ABCDE"

The stringbuilder has the capability of specify a capacity, but this
does nothing just to set an initial size.
If I put a string larger than its capacity it just grows.

So, is there any special class that does this?

If there isn't. Can I inherit from string and create a class that does
this?

Thanks in advance,

 

[Deckarep]

Let's see...

You can't inherit the String class because it's sealed but you can use
composition to enhace it.

This shouldn't be hard at all...this might be a good starting point:

class FixedString
{
private int m_iSize;
private String m_sInternal;

public FixedString(int size)
{
m_iSize = size;
}

public FixedString(String str)
{
m_sInternal = str;
m_iSize = str.Length;
}

public FixedString(String str, int size)
{
m_sInternal = str;
m_iSize = size;
}

public override String ToString()
{
if (m_iSize == 0)
return m_sInternal;

return m_sInternal.Substring(0, m_iSize);
}
public int Size
{
get { return m_iSize; }
set { m_iSize = value; }
}

}

Usage: FixedString myFixedString = new FixedString("ABCDEF");

Console.WriteLine( myFixedString.ToString() ); //just outputs the
full string

myFixedString.Size = 3;

Console.WriteLine( myFixedString.ToString() ); //outputs "ABC"

OR

FixedString myFixedString = new FixedString("ABCDEF", 4); //This adds
the string AND sets the size in one easy and convenient step
Console.WriteLine( myFixedString.ToString() ); //outputs "ABCD"


Depending on specifically what you want this may or may not work but
you get the idea. And there's always more than one way to skin a cat
so this way of doing it is just a start...I'm sure there's better or
more elegant solutions.

Good luck!

-Ralph

 

[RobinS]

Please note that the String class is Immutable. So if you have a variable
defined as one string, and you change the string, it actually creates a
whole new string object.

Also, with the StringBuilder, you can specify the starting size.

Robin S.
---------------------------------------

 

[Ignacio Machin \( .NET/ C# MVP \)]

Hi,


|
| If there isn't. Can I inherit from string and create a class that does
| this?

Well both string and StringBuilder are sealed so you cannot inherit from
them. you could always create your own class and just use a StringBuilder as
the storage.

 

[craigkenisston]

May be I should tell my problem rather than my lame solution-wanna-be.

I have an application for which I don't have control on the user
input. It is data from the web, from which I have no control, there's
no "form" to input this data, but it is received as parameters.
I made the database with enough space, but since I can't control it
some time, the string overflows the column width and causes a database
error, as it should be.
(Please, don't ask me to change a bit on the database, I want a
solution on the application).

Is there an automated way to control this? May be there's an option
somewhere in the ado.net control that I don't know.
I just don't want to write :
mystring = mystring.substring(0, Math.Min(mystring.lengh,
the_column_size_in_the_table);

for every string, every where.

If I go to the custom class, which I had done already and btw, also
called it "fixedstring", I'd have to re-write the logic on string
assignments everywhere, too !

 

[Deckarep]

Sounds like some weird requirements

Perhaps you can just extend whatever ado.net control that you are
using and capture the string data at a certain point, truncate it as
needed....then let it submit to the database.

This way you'd only be enhancing that control in one place and you are
done.

-Ralph

 

[Ignacio Machin \( .NET/ C# MVP \)]

Hi,

| May be I should tell my problem rather than my lame solution-wanna-be.
|
| I have an application for which I don't have control on the user
| input. It is data from the web, from which I have no control, there's
| no "form" to input this data, but it is received as parameters.
| I made the database with enough space, but since I can't control it
| some time, the string overflows the column width and causes a database
| error, as it should be.

That is super common I think,
just check for the size of the column

if ( varString.Length > 50 )
myCommand.Parameters["StringColumn"] = varString.Substring( 0, 50);
else
myCommand.Parameters["StringColumn"] = varString;



| (Please, don't ask me to change a bit on the database, I want a
| solution on the application).

Not at all


With the above code you only have to modify one piece of code

 

[Quoc Linh]

May be I should tell my problem rather than my lame solution-wanna-be.

I have an application for which I don't have control on the user
input. It is data from the web, from which I have no control, there's
no "form" to input this data, but it is received as parameters.
I made the database with enough space, but since I can't control it
some time, the string overflows the column width and causes a database
error, as it should be.
(Please, don't ask me to change a bit on the database, I want a
solution on the application).

Is there an automated way to control this? May be there's an option
somewhere in the ado.net control that I don't know.
I just don't want to write :
mystring = mystring.substring(0, Math.Min(mystring.lengh,
the_column_size_in_the_table);

for every string, every where.

If I go to the custom class, which I had done already and btw, also
called it "fixedstring", I'd have to re-write the logic on string
assignments everywhere, too !

Of course there is ;-). The dataset you are putting in has definition
of the column length it requires:

use these properties for your automation:

ds.Tables[0].Columns[stringColumnNamehere].MaxLength
ds.Tables[0].Columns[stringColumnNamehere].DataType

Here's a sample code:

string SourceString = "some value you read in"; //set for testing
purpose
string OutputString; //Need to be here for testing purpose
//Set length of string requirements
// only need to do this once
// Not sure why dataset doesn't have this after read in from table. I
think using
// FillSchema might do the trick (recalled from memory)
acDs.Tables[0].Columns[2].MaxLength = 100;
for (int i=0; i<acDs.Tables[0].Columns.Count; i++)
{
DataColumn col = acDs.Tables[0].Columns;
switch (col.DataType.FullName)
{
case "System.Int32":
case "System.Decimal":
//specific doe to handle numbers, if any
break;
case "System.DateTime":
//specific code to handles datetime, if any
break;
case "System.String":
if (col.MaxLength > 0)
OutputString = SourceString.Substring(0,
col.MaxLength <
SourceString.Length ? col.MaxLength :

SourceString.Length);
else
{
//Either throw an exception or don't take length into
consideration
OutputString = SourceString;
//throw new ArgumentException("String column length is not
defined", col.ColumnName);
}
break;
}
}

HTH,
Quoc Linh